The metaphosphate anion has attracted steady interest since 1955 [1] in connection with wide applications in phosphorylation reactions.[2] It has relevance in biochemistry in particular with respect to ATP hydrolysis.[3] However, despite considerable efforts, monomeric metaphosphates and other dioxophosphoranes are only known as transient species in solution and their existence can be inferred from trapping experiments. [2][3][4] Their high reactivity arises from the powerful electrophilic character at the phosphorus center. Several approaches have been tested to stabilize these highly reactive species. Kinetic stabilization by steric protection [5] proved to be ineffective for dioxophosphorane and led to products that resulted from the insertion of the PO 2 moiety in a neighboring group.[6] The electrophilicity and the tendency to expand the valence shell were exploited for their stabilization as Lewis salts. This strategy allowed only spectroscopic characterization by 31 P NMR in a few cases. [7] Thus, the chemistry of dioxophosphorane suffers from a paucity of information and new approaches to stabilize and enable deeper investigation are highly desirable. This work describes the first isolation and full characterization, including X-ray structural analysis, of stabilized metaphosphonate.We have developed a novel and successful route to ruthenium-stabilized monomeric metaphosphonate by oxidation of a nucleophilic terminal phosphinidene complex of ruthenium. As recently described by Lammerstma and coworkers, the terminal phosphinidene ruthenium complexes [(h 6 -p-cymene)Ru(PR 3 )(PMes*)] (3 a: R = Cy, 3 b: R = Ph [8] ) are formed as dark green solids by the reaction of the primary phosphane complex [(h 6 -p-cymene)RuCl 2 (PH 2 Mes*)](1; pcymene = 4-methyl-iso-propylbenzene; Mes* = 2,4,6-tri-tertbutylphenyl) with two equivalents of 1,8-diazabicyclo[5-4-0]undec-7-ene (DBU) in the presence of PR 3 as a stabilizing ligand (R = Ph, Cy).[8] Alternatively, treatment of [(h 6 -pcymene)RuCl 2 (PR 3 )] (2 a: R = Cy, 2 b: R = Ph) and PH 2 Mes* with DBU affords 3 in high yields (Scheme 1).